Shaft for electrical switch and method of making



Dec. 12, 1967 c. J. HOLTKAMP SHAFT FOR ELECTRICAL SWITCH AND METHOD OF MAKING Filed Oct. 11, 1965 United States Patent 3,357,205 SHAFT FOR ELECTRICAL SWITCH AND METHOD OF MAKING Calvin J. Holtkamp, Mansfieid, Ohio, assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 11, 1965, Ser. N 494,355 8 Claims. (Cl. 64-1) ABSTRACT OF THE DISCLOSURE A twisted control shaft of D-shaped cross-section in which the tendency of the shaft to deflect out of a straight line is avoided by either turning down a center section so that its center line of mass is coincident with the longitudinal axis symmetrical to the circular surface areas of the D-shaped end portions, or by applying an oppositely or offsetting force to maintain the straightness of the shaft where the entire length of the shaft is left in a D-shaped cross section.

This invention relates to a shaft for electrical switches and controls of the character used on domestic appliances.

One common cross sectional configuration used for switch and control shafts for domestic appliances such as cooking ranges is a D-shape which may be formed by taking a circular shaft and milling a fiat on one side. Occasionally it is desirable that the flat at one end of the shaft be angularly displaced from the flat along another portion of the length of the shaft. Typically, a special shaft of this character is made by milling separate flats at the two locations, which results in a relatively high piece cost for the shaft.

Accordingly, it is an object of this invention to provide a shaft having angularly displaced flats at less cost than with the previous way.

According to this invention, a shaft having angularly displaced flats along separate portions of its length is made by applying a torsional stress to a standard D stock shaft, to strain the shaft beyond its elastic limits, and working the shaft either before or during the application of the torsional stress to place the shaft in a condition that after the removal of the torsional stress the longitudinal axis of the shaft substantially coincides with its original position. Expressed in another way, the method of the invention is carried out by simply twisting a D stock shaft the required number of degrees while taking the proper steps to insure that after the twisting is accomplished the shaft is not bent or deflected.

The working of the shaft to insure straightness after the twisting operation includes two ways as presently contemplated. The first and preferred way is to turn down an intermediate portion of the length of the standard D stock shaft to provide a reduced diameter center portion which is circular is cross section and has its longitudinal axis coinciding with the original longitudinal axis of the original circular stock. Then, when the twisting operation is carried out by applying the twisting forces to the opposite D-shaped sections, the torsional strain will occur almost wholly in the turned down intermediate section. Because the intermediate portion longitudinal axis coincides with the center of mass of the circular section, the longitudinal axis remains in its original position after twisting since the stresses which tend to cause deflection after the twisting forces are released are not present. With this method, the flats of the separate lengthwise portions of the shaft remain as flat plane forms. Also it is preferred that the turned-down section of length have small radius fillets at the junctures of the round section and D-shaped section so that stress concentration areas are avoided.

The other way of carrying out the method according to the invention is to twist a D shaft without first turning down an intermediate section to a round shape, but applying a force while the twisting is being carried out which will compensate for the tendency of the shaft to assume a bent form when it is released. The reason for applying a compensating force of a bending character during the twisting operation is that a D shaft tends to twist about the center of mass of the section rather than about a longitudinal axis at the center of the circular surface portion of the shaft. Hence, if a D shaft is simply twisted by holding one end stationary while rotating the opposite end to effect the desired twist, when the shaft is released from the holding clamps the shaft will deflect as a result of the tendency of the shaft to twist about a line coincident with its center of mass at the various sections.

A control shaft according to the invention comprises successive first, second and third lengthwise-extending portions, the first and third portions being of non-circular transverse cross-section in part at least, the second portion including a length thereof torsionally strained beyond its elastic limit to effect the angular displacement of the first and third portions to positions in which their surfaces are out of registering alignment in a longitudinal direction.

The invention will be described further in connection with the accompanying drawing wherein:

FIG. 1 is an isometric view of a D shaft in untwisted form and ready to be turned down in an intermediate portion;

FIG. 2 is an isometric view of the shaft with its center portion turned down, and with clamping collets secured for the twisting operation;

FIG. 3 is an isometric view of the shaft after twisting, and with several members adapted to fit on the angularly displaced portions of the shaft shown in exploded relation before assembly to the shaft;

FIG. 4 is an isometric view of a uniform section D shaft before twisting with collets secured for a combined bending and twisting operation; and

FIG. 5 is an isometric view of the twisted D shaft after removal of the collets, this view showing the shaft rotated relative to its FIG. 4 position to better portray its appearance.

The D shaft of FIG. 1 includes a spindle end 10 which is circular in cross section and has its axis coincident with the longitudinal axis of the circular surface portion of the D shaft. The length of the D shaft proper is divided for purposes of description into a first end portion 12 adjacent the spindle, a second or intermediate portion 14, and an opposite end portion 16.

The D shaft of FIG. 1 is placed in a lathe (not shown) with the lathe centers aligned with the D shaft axis so that the cutting tool 18 turns down the intermediate portion 14 about the shaft axis. The turned down portion 14 is round in transverse section when finished with its axis aligned with the axis of the spindle 1t) and the longitudinal axis of the circular surfaces of the end portions 12 and 16. The corners 20 of the cutting tool are provided with radii which leave a small radius fillet 22 at each end of the intermediate portion 14.

Referring to FIG. 2, a pair of clamps 24 and 26 are positioned on the end sections 12 and 116, respectively, preparatory to twisting the shaft. The arrows adjacent the clamps in FIG. 2 indicate the relative direction of twist between the two clamps.

After the D shaft has been twisted to the desired degree it appears, for example, as in FIG. 3 in which a twist of about has been imparted to the shaft. Accordingly, the flats on the end sections 12 and 16 have been angularly displaced with respect to each other 129. The flat plane surfaces of the end portions 12 and 16 maintain their flatness throughout the twisting operation since the twist imparted to the shaft is taken up substantially entirely by the turned-down intermediate portion 14. Since the longitudinal axis and the mass centerline axis of the reduced portion are coincident, no defiection of the intermediate portion occurs. It will be appreciated of course that the torsional stress applied to the intermediate portion 14 greatly exceeds its elastic limits of torsion so that the shaft is torsionally strained after the clamps are removed. The shaft may be of brass or any other suitable material having sufiicient ductility to accommodate the working operations carried out upon it. After the shaft has been formed as shown in FIG. 3, the members such as the cam element 28 and the knob 30', for example, are fitted upon the portions 12 and 16, respectively, and the end spindle 10 may be journalled in a bore to support that end of the shaft carrying the cam 28.

A twisted shaft such as disclosed may be used in connection with a thermal cycling switch, for example, for controlling cooking temperatures. Accordingly, accuracy in temperature adjustment demands that the shaft be straight to insure that wobble of the cam 2% during r tation of the shaft is precluded.

A way of making a twisted shaft which does not re quire turning down an intermediate portion will be described in connection with FIGS. 4 and 5. Again the shaft includes an end spindle 40 and the length is divided for descriptive purposes into opposite end portions 42 and 46 and an intermediate portion 44. The clamps 48 and 50 are installed upon the end portions. The relative direction of twist imparted to the shaft by the clamp 50 is indicated by the arrow adjacent the clamp. While clamp 53 is being rotated as shown, the clamp 48 is cocked (i.e. rotated very slightly about the illustrated axis 52 which is perpendicular to the longitudinal axis of the shaft). The purpose of cocking clamp 48 while the shaft is being torsionally strained is to impart a bending moment to the shaft. This bending moment counters the bending movement imposed upon the shaft by its tendency to twist about its center of mass rather than about the axis of the curved surface portions of the shaft. Thus, after the clamp 48 and 50 are removed, the axis remains sub stantially straight.

The direction in which the force is to be applied at the one end of cocking the clamp 48 is a function of the degree of twist to be imparted to the rod. In the case of the 180 twist as shown in FIGURE 5, the clamp 48 is cocked as shown in FIGURE 4, which is the same as applying a linear bending force in the direction indicated by the arrow 54 at the end portion 42, which corresponds to the Z axis of the three coordinate axes shown. If however, the shaft of FIG. 4 is to have only a 90 twist imparted to it, so that the end portions 42 and 46 are angularly displaced only 90, then the linear bending force should be directed as shown by arrow 56, which is 45 removed from the arrow 54 and lies in the Y-Z plane. This linear bending force line 56 may of course be equivalently applied by cocking the clamp 48 about an axis 45 removed from the axis 52. For degrees of twist other than those described, the bending moment is of course shifted in accordance with the direction of deflection of the shaft occurring as determined by twisting the shaft Without applying any corrective bending moment.

Numerous advantages are available from a method according to the invention. The invention provides a relatively simple means for obtaining any specifically desired angular displacement of the flats up to 180. Between 180 and 360, the shaft may simply be twisted in the opposite direction up to 180. Standard D stock shafts which are less costly than round stock may be used. Additionally, the two milling operations required 011 round stock to obtain two angularly displaced flats are eliminated and replaced by a single twisting operation a 4 in the case of the embodiment of FIGURES 4 and 5, and the turning down operation and twisting operation in the case of the FIGS. l-3 embodiment. Additionally, the previous requirements of relatively strict tolerances when the flats were milled out of round stock are substantially avoided.

I claim as my invention:

1. A control shaft comprising:

first, second and third lengthwise extending portions;

said first and third portions being of non-circular transverse cross section, in part at least, to mate with a correspondingly cross-sectionally shaped member, said cross-section of said first and third portions including one surface area symmetrical to the longitudinal axis of the portion, and a remaining surface area which is substantially fiat whereby the longitudinally extending center line of mass of said first and third portions is offset from the respective longitudinal axis;

said second portion including a length thereof torsionally strained beyond its elastic limits to effect angular displacement of said first and third portions to positions in which their said fiat surface areas are out of registering alignment, and in which their said longitudinal axes are aligned.

2. A rotary switch shaft comprising:

first, second and third lengthwise extending portions, at

least said first and third portions being D shaped in transverse cross section for insertion in D shaped apertures of elements to be mounted on said first and third portions, the circular parts of said D- shaped cross-sections of said first and third portions being symmetrical to the longitudinal axis of said portion, whereby the longitudinally extending center line of mass of said first and third portions is offset from the respective longitudinal axis;

said second portion including a length thereof torsionally strained beyond its elastic limits to effect angular displacement of said first and third portions to positions in which the flats of their D shaped surfaces are out of registering alignment, and in which their said longitudinal axes are aligned.

3. A rotary switch shaft according to claim 2 wherein:

said second portion is substantially circular in transverse cross section and of reduced radius relative to the radius of said circular parts of the surfaces of said first and third portions, the axis of said second reduced radius portion being aligned with the said longitudinal axes of the circular part of the surfaces of said first and third portions.

4. A rota1y shaft according to claim 2 wherein:

said second portion includes fillets at its opposite ends where said second portion joins said first and third portions.

5. A rotary shaft according to claim 2 wherein:

said second portion is D shaped in transverse cross section and constitutes an integral continuation of said first and third portions, all of said portions being torsionally strained beyond their elastic limits and all of the circular surfaces of said first, second and third portions coinciding with the circumferential surface of an imaginary right cylinder having an axis corresponding to the axis of the circular portions of said D shaped sections.

6. The method of making a rotary switch shaft having angularly displaced fiat portions at longitudinally spaced locations from a shaft having a D shaped transverse cross section including a circular surface portion and a flat surface portion in which the flat of the shaft originally lies in a plane:

restraining one end of said shaft length from rotation while;

rotating the other end of said shaft to torsionally stress an intermediate portion of said shaft beyond its elastic limits;

said one and said other ends being disposed, for the application of said torsional stress, relative to the longitudinal axis of said circular surface portions of said shaft, to assume angularly displaced final positions in which said longitudinal axis coincides with the axis of an imaginary right cylinder having circumferential surfaces coinciding with circular surface portions of said end portions of said shaft.

7. The method of making a rotary switch shaft from shaft stock having a D shaped transverse cross section for its length:

turning down an intermediate portion of said shaft stock to a substantially circular cross section having an axis longitudinally aligned with the longitudinal axis of the circular surface portions of said shaft; and

applying torsional stress to the opposite ends of said shaft after the intermediate portion has been turned down to stress said intermediate portion torsionally beyond its elastic limits to eifect angular displacement of the fiat portions of said opposite ends relative to each other.

8. The method of making a rotary switch shaft having angularly displaced flat portions at longitudinally spaced locations on said shaft comprising:

holding a piece of shaft stock having a D shaped transverse cross section which is uninterrupted for the length of said shaft in a clamping collet at one end and in another clamping collet at an opposite end;

rotating one of said collets in one direction relative to the other to apply a torsional stress exceeding the elastic limits of torsion of the portion of said shaft between said collets; and

shifting one of said collets out of its original position during said application of said torsional stress to impose a deflection stress counter to the deflection stress arising from the tendency of incremental sections of said D shaped shaft to twist about their respective centers of mass rather than twisting about the longitudinal axis of the circular surface portions of said shaft.

References Cited UNITED STATES PATENTS 833,153 10/1906 Blakeslee 64-l5 1,157,148 10/1915 Bond 64-15 2,585,844 2/1952 Romero 641 2,929,434 3/ 1960 Barnes 72299 3,067,800 12/1962 Gogan 72299 HALL C. COE, Primary Examiner. 

1. A CONTROL SHAFT COMPRISING: FIRST, SECOND AND THIRD LENGTHWISE EXTENDING PORTIONS; SAID FIRST AND THIRD PORTIONS BEING OF NON-CIRCULAR TRANSVERSE CROSS SECTION, IN PART AT LEAST, TO MATE WITH A CORRESPONDINGLY CROSS-SECTIONALLY SHAPED MEMBER, SAID CROSS-SECTION OF SAID FIRST AND THIRD PORTIONS INCLUDING ONE SURFACE AREA SYMMETRICAL TO THE LONGITUDINAL AXIS OF THE PORTION, AND A REMAINING SURFACE AREA WHICH IS SUBSTANTIALLY FLAT WHEREBY THE LONGITUDINALLY EXTENDING CENTER LINE OF MASS OF SAID FIRST AND THIRD PORTIONS IS OFFSET FROM THE RESPECTIVE LONGITUDINAL AXIS; SAID SECOND PORTION INCLUDING A LENGTH THEREOF TORSIONALLY STRAINED BEYOND ITS ELASTIC LIMITS TO EFFECT ANGULAR DISPLACEMENT OF SAID FIRST AND THIRD PORTIONS TO POSITIONS IN WHICH THEIR SAID FLAT SURFACE AREAS ARE OUT OF REGISTERING ALIGNMENT, AND IN WHICH THEIR SAID LONGITUDINAL AXES ARE ALIGNED. 